Suramin: A polysulfonated compound that inhibits the binding of HIV-1 gp120 to GalCer/sulfatide and blocks the CD4-independent pathway of HIV-1 infection in mucosal epithelial cells

Glycolipids as potential binding sites for HIV: topology in the sperm plasma membrane in relation to the regulation of membrane fusion

Although human sperm cells can bind human immunodeficiency virus (HIV-1), they lack CD4, galactoceramides (GalCer) and sulfogalactoceramides (SGalCer) as gp120 receptors. However, sperm specific glycolipids (sulfogalactosylalkylacylglycerol (SGalAAG) and galactosylalkylacylglycerol (GalAAG)) are structurally closely related to SGalCer and GalCer as predicted by computer simulated molecular modelling. SGalAAG and GalAAG are exclusively localized in the outer leaflet of the human sperm plasma membrane, and therefore we tested whether they could serve as alternative receptors for the gp120. Purified SGalAAG and GalAAG had similar affinities to recombinant gp120 as the hydroxy fatty acid (HFA) SGalCer and HFA-GalCer respectively. However, nonhydroxy fatty acid forms of (S)GalCer, galactosyldiacylglycerol and the deacylated (sulfo)galactosyllipids did not recognize recombinant gp120. Data obtained by surface pressure experiments revealed that the lipid monolayers that contained HFA-GalCer or GalAAG resulted in a similar significant penetration of recombinant gp120 in the monolayer. The penetration was a factor of two lower in monolayers with HFA-SGalCer or SGalAAG. The binding of recombinant gp120 to human sperm cells colocalized with GalAAG and could be blocked with monoclonal antibodies against galactolipids. The possible relevance of gp120 binding to glycolipids for HIV entry in sperm cells is discussed.

Synthetic soluble analogs of galactosylceramide (GalCer) bind to the V3 domain of HIV-1 gp120 and inhibit HIV-1-induced fusion and entry

Galactosylceramide (GalCer) is an alternative receptor allowing human immunodeficiency virus (HIV)-1 entry into CD4-negative cells of neural and colonic origin. Several lines of evidence suggest that this glycosphingolipid recognizes the V3 region of HIV-1 surface envelope glycoprotein gp120. Since the V3 loop plays a key role in the fusion process driven by HIV-1, we decided to synthesize soluble analogs of GalCer with the aim to develop a new class of anti-HIV-1 agents that could neutralize HIV-1 infection through masking of the V3 loop. We describe a short route, in three steps, for the synthesis of soluble analogs of GalCer, using unprotected lactose as the starting sugar. The analogs were prescreened in an assay based on the interaction between a V3 loop-derived synthetic peptide and [3H]suramin, a polysulfonyl compound displaying high affinity for the V3 loop. One of the soluble analogs, i.e. CA52(n15), strongly inhibited the binding of [3H]suramin to the V3 peptide, with an IC50 of 1.2 microM. This molecule was also able to inhibit [3H]suramin binding to recombinant gp120 with similar activity. Using a competition enzyme-linked immunosorbent assay with highly specific anti-gp120 monoclonal antibodies, the region recognized by CA52(n15) could be mapped to amino acids 318-323, which corresponds to the highly conserved consensus motif GPGRAF. Interestingly, the region recognized by suramin, i.e. IQRGP-R-F, was partially overlapping this motif. CA52(n15) was able to inhibit HIV-1-induced cell fusion as well as HIV-1 entry into both CD4(+) and CD4(-)/GalCer+ cells. A structure-activity relationship study showed that: (i) the antiviral activity of soluble analogs of GalCer correlates with V3 loop binding, and (ii) the hydrophobic moiety of the molecule plays an important role in this activity. Taken together, these data show that synthetic analogs of GalCer can inhibit HIV-1 entry into both CD4(-) and CD4(+) cells through masking of the V3 loop.